1. Field of the Invention
The present invention relates to a positive photoresist composition having satisfactory sensitivity and definition. In particular, it relates to a positive photoresist composition which can give, in a process for forming a resist pattern using a large-diameter substrate, satisfactory pattern shapes in which dimensional changes over a wide range of the surface of the substrate are minimized, and to process for forming resist pattern using the composition.
2. Description of the Related Art
Positive photoresist compositions comprising an alkali-soluble resin and a quinonediazide ester have been satisfactorily applied in practice for the production of semiconductor devices and liquid-crystal display devices, since they have excellent definition, sensitivity and etching resistance.
In the current manufacture of ultralarge-scale integrated circuit (Ultra LSI), a high definition of not more than half a micron, for example, of 0.4 xcexcm or 0.3 xcexcm is required. There are, therefore, demands on photoresist compositions which can form a resist pattern satisfactory in definition, exposure margin, focal depth range properties and having a good shape.
In development, a puddle development technique is generally applied, in which a developer is applied all over the surface of a substrate from a developer-supplying nozzle disposed above the vicinity of the substrate""s center, allowing the substrate to stand for several seconds and rotating it to remove the developer on the substrate""s surface through centrifugal force generated by the rotation of substrate. The developer, therefore, is in contact with the substrate for somewhat longer in its center than in its periphery.
The use of a large-diameter, 8-to 12-inch substrate has been considered instead of a conventional 6-inch substrate, in order to enhance the throughput and productivity of semiconductor chips. In such a large-diameter substrate, however, the puddle developing technique invites tapering of a pattern and reduction in thickness of a resultant film in the center of substrate, which results in deteriorated yield of production.
In particular, when a resist pattern of not more than half a micron is formed, twist of pattern formation occurs in the substrate""s center and the yield is reduced, and hence the enhancement of the throughput can hardly be achieved.
On the other hand, a variety of high-definition positive photoresist compositions have been reported which are directed to quinonediazide esters as photosensitizers (e.g., Japanese Patent Laid-Open Nos. 8-245461, 6-167805, 7-152152, 7-159990, 7-168355, 7-175213, 7-219220, 7-261382, 7-129255, 8-146602, 8-254824, 8-339079, 9-15854, 9-96904, 9-110755, 9-110757, 9-110760, 9-110762, 9-127690, 9-179293, 9-258437, 9-281702, 9-286751, 9-286752, 9-286753, 9-291054, 9-291055 and 9-291056).
These compositions exhibit high definition but are still insufficient to reduce dimensional changes in resist patterns on the surface of a substrate, and are still insufficient for the application to a large-diameter substrate in order to enhance the throughput.
Demands have, therefore, been made to provide positive photoresist compositions which can form a resist pattern of not more than half a micron having a good shape whose in-plane dimensional changes are minimized over a substrate""s surface.
Accordingly, it is an object of the present invention to provide a positive photoresist composition which can form a resist pattern of not more than half a micron having a good shape in which dimensional changes over a wide range of the surface of a substrate are minimized, and to provide, particularly in a resist pattern forming process using a large-diameter substrate, a process for forming a resist pattern using the composition.
After the intensive investigations, the present inventors have solved the above problems of conventional techniques.
To be more specific, the present invention provides a positive photoresist composition comprising (A) an alkali-soluble resin, (B) a photosensitizer containing a quinonediazide ester of a compound of the following formula (I): 
wherein each of R1 and R2 is independently a methyl group or an ethyl group, and (C) at least one of phenol group-containing compounds giving an elution time ranging from 6 to 30 minutes in high performance liquid chromatography determined under the following conditions: eluent: a mixed solvent of water/tetrahydrofuran/methanol=40/24/36 (by weight); column: 4.6 mm (diameter)xc3x97150 mm (length) containing 5 xcexcm silica gel as a filler (carbon content being about 15%); column temperature: 45.0xc2x0 C.; supply rate of eluent: 0.700 ml/min.
The compound represented by the formula (I) in the composition may be a compound of the following formula: 
In addition, the compound represented by the formula (I) in the composition may be a compound of the following formula (Ib): 
In the above composition, the content of Ingredient (C) may preferably range from 5% to 50% by weight relative to Ingredient (A).
The phenol-group containing compound, Ingredient (C), of the aforementioned composition may be at least one compound selected from: 
The invention provides, in another aspect, a process for forming a resist pattern comprising the steps of:
(1) coating the aforementioned positive photoresist composition onto a substrate having a diameter of 8 to 12 inches, and drying the coated substrate to form a resist film,
(2) subjecting the resist film to selective exposure through a mask,
(3) heating the exposed resist film, and
(4) removing the resist film at exposed positions by an aqueous alkali solution.